With the rapid development of flexible display technology in recent years, many display panel manufacturers have exhibited their own prototypes, and actively deployed their flexible display production lines and mass production lines simultaneously. Flexible display products have been gradually developed from a research stage to a mass production stage.
A flexible substrate is a foundation of the flexible display technology. At present, there are mainly two types of flexible substrates, i.e., a polyimide (PI) substrate with a sandwich structure, and a single-layered PI substrate. When both of the above two PI substrates are coated with PI, an uneven PI diffusion may result in a problem of uneven film thicknesses at edges of the PI substrates. Due to the uneven thickness of PI at the edges of the substrates, defects invisible to naked eyes, such as residual solvents, incomplete curing and holes, may be generated during drying and curing. These defects may be turned into defects visible to the naked eyes during the subsequent process, which affects a yield rate of the PI substrates.